Effects of Microstructure on Material Behaviors of Solder Alloys

摘要:

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The leading candidates for replacing lead-contained solders are near ternary eutectic Sn/Ag/Cu alloys. The electronic industry has begun to study both the process behavior and the reliability assessment of these alloys in detail to figure out their applicability to electronic devices and products. In recent publications, the solidification behavior and the fatigue life of the accelerated thermal cycle test have been reported in terms of microstructure variations such as the formation of large Ag3Sn plates and their effects. In this study, coupon type bulk specimens have been made for uniaxial tensile test by casting. To consider the effects of microstructure, casting cooling rates were controlled to 0.02-2.0 oC/sec. Eutectic Sn/Pb and near eutectic lead-free solder materials – Sn/Ag/Cu and Sn/Cu alloys – were used in mechanical testing. Also, nanoindentation tests were performed to
measure Young’s modulus of materials having different microstructures. Tensile tests were performed at 3 different strain rates and then acquired 0.2% offset proof stress, ultimate tensile strength and elongation to failure.

摘要: The effects of alloy chemistry and heat treatment on the microstructure and mechanical properties of Ti-Nb-Zr-Mo-Sn near  type titanium alloys have been investigated. Near β titanium alloys consisting of non-toxic alloying elements Mo, Nb, Zr, Sn possess a low Young’s modulus, and moderate strength and plasticity. As the hot rolled TLM alloy (Ti-25Nb-3Zr-3Mo-2Sn) possesses high strength and low Young’s modulus a detailed investigation is performed for this alloy. Solution treatment of the hot rolled TLM alloy reduces strength and increases ductility without affecting the Young’s modulus. Ageing of the solution treated TLM alloy reduces elongation and increases the Young’s modulus with little change in strength. Both solution treated and aged conditions show features of two stage yielding associated with a strain induced martensitic transformation.

摘要: Due to the advantages of FRP composite such as corrosion resistance, light weight, high specific strength and stiffness, flexibility, etc., the use of FRP composite in construction sites is increasing steadily. Especially, high corrosion resistance is a very strong point of FRP composite. Although the FRP composite has many advantages, the material properties of FRP composite under various environmental conditions at the construction sites are not well investigated. In this paper, we present the results of experimental investigations of FRP composite experiencing freezing and thawing cyclic temperature. In this investigation, we performed experimental studies to find the stress versus strain characteristics of FRP composite experiencing freezing and thawing cyclic temperature variation. In the experimental program, strength and stiffness of the pultruded FRP composite specimens under uniaxial tension affected by the freezing and thawing temperature change mechanism are evaluated and the results are discussed.

摘要: The influence of physical aging on mechanical properties of glassy polymers was investigated in this paper. After annealing above Tg to release the previous thermal and stress history, the polymethyl methacrylate (PMMA) samples were quenched to 27°C, aged for various times (ta), and were then stretched at the same temperature by two ways: (1) step stresses with four different magnitudes varying from 15MPa to 30MPa; (2) constant rate stretch up to fracture. The physical aging effect was monitored by measuring the initial instantaneous elastic modulus (E) and the fracture strength (σf) from the stress-strain curves as a function of ta up to 1368h. It is shown that both E and σf of the material increase with aging time and approach to their asymptotic values, which satisfy the KWW rule, while the isochronous creep compliance decreases with log ta in a linear manner within the aging time range considered in this paper.

摘要: Functionally graded materials (FGM) are characterized by a gradual change in the volume fractions of two or more components as a function of position along certain dimensions. FGM has been introduced as an alternative to laminated composites where a mismatch in properties across each layer interface is the origin of stress concentration and a source of delamination/failure. In addition, the use of natural wood fibres as reinforcement has the advantage of easy manufacturing, low cost, biodegradability, negligible health hazards and high specific properties. Using short fibres in a controlled manner to produce functionally graded composites can provide more balanced properties and lead to improved stiffness/strength properties across thickness. The aim of this paper is to evaluate the mechanical behavior of functionally graded natural fibre composites. To study the effect of composite property variation, the functionally graded composite is divided into a number of homogeneous layers in order to evaluate the mechanical behavior. In particular, the effect wood fibre content variation across thickness on the tensile properties of the composites is presented.

摘要: A Ti-25Ta-25Nb β-type titanium alloy was subjected to thermo-mechanical processing and testing with the aim to observe the twinning deformation mechanism. Data concerning the evolution of twinning versus stress was obtained by SEM and micromechanical testing. Mechanical properties of the investigated alloy were also evaluated